Structural Bolting Assemblies according to EN 14399

EN 14399-1…10 High Strength Structural Bolting assemblies for preloading.

• UNI EN 14399-1:2005 General Requirements

• UNI EN 14399-2:2005 Suitability test for Preloading

• UNI EN 14399-3:2005 System HR. Hexagon bolt and nut assemblies

• UNI EN 14399-4:2005 System HV. Hexagon bolt and nut assemblies

• UNI EN 14399-5:2005 Plain washers

• UNI EN 14399-6:2005 Plain chamfered washers

• UNI EN 14399-7:2008 System HR. Countersunk head bolt and nut assemblies

• UNI EN 14399-8:2008 System HV. Hexagon fit bolt and nut assemblies

• UNI EN 14399-9:2008 System HR or HV. Direct tension indicators for bolt and nut assemblies

• UNI EN 14399-10:2009 System HRC. Bolt and nut assemblies with calibrated preload

Structural Bolting according to EN 14399

There are three approved technical solutions for High-Strength Structural Bolting in

Europe, as outlined below

HR ASSEMBLIES HV ASSEMBLIES HRC ASSEMBLIES

GENERAL REQUIREMENTS EN14399-1

SUITABILITY TEST FOR PRELOADING EN14399-2 , additional tests on request

BOLT AND NUT EN14399-3 EN14399-7 EN14399-4 EN14399-8 EN14399-10

BOLT MARKING HR HR HV HVP HRC

NUT MARKING HR HR HV HV HR or HRD

PROPERTY CLASS 8.8/8 -

10.9/10

8.8/8 -

10.9/10

10.9/10 10.9/10 HR or HRD

WASHER(S) EN 14399-5 or EN14399-6

WASHER MARKING H

DIRECT TENSION INDICATOR WASHER LEANED AGAINST THE

NUT AND/OR THE BOLT

EN14399-9

AT USER’S

DISCRETION

DTI MARKING H8 or H10 H10

MARKING OF THE WASHER LEANED AGAINST THE NUT

HN MARKING OF THE WASHER LEANED AGAINST THE BOLT HB NA HB

HOT DIP GALVANIZING AND BLACK OXIDE ARE THE MOST COMMON COATINGS

HR System

• diameters from M12 to M36

• Wrench according to Large ISO series

(except M20 and M12)

• Oversized under head radius

connections

• Partial thread ISO 888

(l variable thread with l=shank)

• nut height as style 1 ISO (~ 0,8d ÷ 0,85d )

• nut proof load larger than ISO 898-2

• 2 heat treated washers (300÷370 HV),

chamfered under head washer

HV System

•diameters from M12 to M36

• Wrench according to Large ISO

series (except M20 and M12)

Oversized under head radius

connections

• Short Partial Thread

(lg. Threaded part depending on

diameter)

•nut height ~ 0,75d ÷ 0,8 d (DIN 6915)

• nut proof load according to ISO 898-2

• 2 heat treated washers (300÷370 HV),

chamfered under head washer

HRC System

•diameters from M12 to M36

• Wrench according to Large ISO

series (except M20 and M12)

• Oversized under head radius

connections

•Partial thread ISO 888

(l variable thread with l=shank)

nut height as style 1 ISO (~ 0,8d ÷ 0,85d )

•2 heat treated washers (300÷370 HV),

chamfered under head washer

• spline end sheared off when preload is

achieved

Depending on the system chosen, the parts can be supplied according to the three classes K0,

K1 e K2 , to which correspond different functional features and tightening methods

K0, K1 and K2 affect the supply terms of the assemblies

SYSTEM

HR HV HRC

K -CLASS

K0 X X X

K1 X X

K2 X X X

Variable

factors

EN14399/3 HR SYSTEM

Hexagon Head

EN14399/4 HV SYSTEM

Hexagon Head

EN14399/10 HRC

SYSTEM (K2-class)

Hexagon/ Round head

K1 K2 K1 K2 K2

Thread

Long thread:

lengths can be

adapted using a

limited number of

codes

Long thread:

lengths can be

adapted using a

limited number of

codes

Short thread: use of

various dimensions

Interchangeability is

limited

Short thread: use of

various dimensions

Interchangeability is

limited

Long thread: lengths can be

adapted using a limited

number of codes

Tightening

methods

The combined

method (torque +

angle ) involves

several tightening

steps and many

workers

The torque method

standardizes the

tightening process

but involves a high

number of workers

The combined method

(torque + angle)

involves several

tightening steps and

many workers

The torque method

standardizes the

tightening process but

involves a high number

of workers

Use of a Shear wrench, The

procedure is simple and

functional (no technical

skills required, erection

time reduced )

Number of

workers

VERY HIGH

HIGH

VERY HIGH

HIGH

LOW

Coatings

Black Oxide/ HDG

According to

specifications

Black Oxide /HDG

According to

specifications

Black oxide /HDG

According to

specifications

Black oxide/HDG

According to

specifications

Black oxide/HDG

According to specifications

Inspections Difficult , according

to 1090-2

Difficult , according

to 1090-2

Difficult , according to

1090-2

Difficult , according to

1090-2

Easy, thanks to the spline

end breaking

Torque method Combined method Direct Tension

Indicator method

TCB method (HRC)

General

Before commencement of preloading the connected components shall be fitted together.

Each bolt assembly shall be brought at least to snug-tight condition with special care being given to avoid

over-tightening. The tightening process shall be carried out from bolt to bolt of the group starting from the most rigid

part of the connection and moving progressively towards the least rigid part. To achieve a uniform snug tight

condition, more than one cycle of tightening may be necessary.

Tooling

The bolts shall be

tightened using a torque

wrench offering a

suitable operating

range. Impact wrenches

may be used for the first

step of tightening only.

Torque wrenches used

in all steps shall be

capable of +/-4%

accuracy and checked

weekly.

For torque wrenches

used in the first step of

the combined

installation method an

accuracy of +/-10% is

required with annual

testing.

Bolts fitted to snug-tight

using a normal size

spanner.

Bolts tightened using

appropriate tooling to

achieve compression of

the DTI.

Shear wrenches do not

require calibration.

Firs tightening step

For the first step the wrench shall be set to a torque

value to achieve about 0.75Mr,i with Mr,i=Mr,i or

Mr,test. The first step shall be completed for all bolts

in one connection prior to commencement of the

second step.

The first step of

tightening to reach a

uniform snug-tight

condition of the fastener

assembly shall be when

initial deformation of the

DTI protrusions begins.

The first tightening step

is achieved using the

shear wrench. When the

outer socket stops

turning and the gearing

backtracks, it allows the

tool to be taken off the

bolt.

Torque method Combined method Direct Tension

Indicator method TCB method (HRC)

Second tightening

step

For the second step, a

torque wrench shall be

set to a torque value of

1.1Mr,i with Mr,i=Mr,2 or

Mr,test.

The torque reference

values Mr,i to be used for

a nominal minimum

preloading force Fp,C are

determined for each type

of bolt and nut

combination used by one

of the following options:

1. Values based on

k-class declared

by the fastener

manufacturer.

2. Values

determined by

Annex H of EN

1090-2 (test to

determine torque

values for

preloaded bolts

under site

conditions)

The second tightening

step involves a specified

part turn to be applied to

the bolt assembly.

The position of the nut

relative to the bolt

thread shall be marked

after the first step using

a marking crayon or

paint so that the final

rotation of the nut

relative to the bolt

thread can be easily

determined.

The additional rotation

during the second step

shall be in accordance

with values given in

table 21 of EN

1090-2:2008.

The second step of

tightening bolts shall be

as EN 14399-9 and

annex J of EN 1090-2;

Indicators are usually

applied under the bolt

head and the bolt is

usually tightened by

rotation of the nut.

A feeler gauge (as

specified in table J.1 of

EN 1090-2) shall be

used to determine

whether the DTI has

compressed in

accordance with the

requirements.

No more than 10% of

the indicators in a

connection bolt group

shall exhibit full

compression of the

indicator.

The second tightening

step is achieved when

the spline end of the

bolt shears off.

Inspection tooling Torque wrenches used for inspections shall be

calibrated and have +/- 4% accuracy.

Feeler gauge used as a

“no-go” inspection tool

NA

Torque method

Combined method

Direct Tension

Indicator method

TCB method (HRC)

Inspection of bolts

during and after

tightening.

General

All connections with preloaded fasteners shall be visually checked after they are initially bolted up and before

commencement of preloading

The number of bolts inspected at random depends on the Execution Class specified

EXC1 to EXC4. If the inspection leads to rejection, all of the bolting assemblies in the

group shall be checked.

The inspection shall be

carried out on 100% of the

bolting assemblies by

visual inspection.

Overall number of bolts to be checked in a class EXC2 structure - 5% for the second

step

EXC3 and EXC4 -10%

for the second step

EXC3 and EXC4 -5% for

the first step and -10%

for the second step

EXC3 and EXC4 -10%

for the second step.

Inspection shall be carried out using a sequential sampling plan according to annex

M of EN 1090-2. If the result of the inspection to sequential type A is negative, the

inspection may be enlarged to sequential type B.

If fasteners are not applied in accordance with the defined methods, the removal

and re-installation of the whole bolt group shall be witnessed.

Torque method

Combined method

Direct Tension

Indicator method

TCB method (HRC)

Inspection at second

step

Specific

The inspection of a bolt

assembly shall be

carried out by the

application of a torque to

the nut using a

calibrated torque

wrench.

The objective is to check

that the torque value

necessary to initiate

rotation is at least equal to

the torque value 1.1Mr,i

with Mr,i=Mr,2 or Mr,test.

After the second step the

marks shall be inspected

with the following

requirements:

1. If the rotation

angle is less than

15° below

specified value,

the angle shall be

corrected.

2. If the rotation is

more than 30°

over specified

angle or the bolt

has failed, the

assembly shall be

replaced.

After the final tightening,

assemblies selected for

inspection shall be checked

to establish that the final

indicator settings are in

accordance with the

requirements specified in

EN 14399-9 and Annex J of

EN 1090-2

Fully tightened assemblies

are identified as those with

the spline sheared off..

Notes

Inspection shall be

carried out between 12

and 72 hours after the

final completion of

tightening of the bolts

concerned